Electronic timepiece

ABSTRACT

An electronic timepiece electronically driven and comprising an electronic circuit formed in a monolithic chip. This electronic circuit comprises passive elements whose resistance element is a MOS-R (metal-oxide-silicon resistor) and whose capacity element is a semiconductor element of MO&#39;&#39;AOS (metal-oxide-Al2O3 oxidesilicon) construction and comprises an active element composed of a bipolar type transistor, and is formed entirely in the monolithic chip.

United States Nishikubo et a1.

atent 1 [451 Sept. 16, 1975 [22] Filed: May 2, 1974 [21] Appl. No.:466,223

[30] Foreign Application Priority Data May 24, 1973 Japan 48-57208 [52]US. Cl. 58/23 R; 357/44; 331/116 M; 318/128; 58/23 A [51] Int. Cl. C04C3/00 [58] Field of Search... 58/23 R, 23 A, 23 AC, 23 D, 58/23 TF, 23 V,28 R, 28 A, 28 B, 28 D;

3,221,231 11/1965 Reich 58/28 R 3,447,051 5/1969 Attwood et a1. 318/1273,568,430 3/1971 Walton 58/23 R 3,602,842 8/1971 Smith 58/23 V PrimaryExaminerJoseph W. Hartary Assistant Examiner-U. Weldon Attorney, Agent,or FirmErnest G. Montague; Karl F. Ross; Herbert Dubno 57] ABSTRACT Anelectronic timepiece electronically driven and comprising an electroniccircuit formed in a mono lithic chip. This electronic circuit comprisespassive elements whose resistance element is a MOS-R(metal-oxide-silicon resistor) and whose capacity element is asemiconductor element of MOAOS (metal-oxide- A1 0 oxide-silicon)construction and comprises an 304 active element composed of a bipolartype transistor,

and is formed entirely in the monolithic chip. [56] References CitedUNITED STATES PATENTS 5 Claims, 11 Drawing Figures 3,124,731 3/1964Eysen et a1. 58/28 A AMPLIFIER E S'SJ' MECHANICAL DISPLAY MECHAN CALELECTRIC TRANSDUCER TRANSDUCER 5 CONTROL DEVICE PATENTEDSEFISEQYS3,905,188

SHKET 1 0f 5 PRIOR ART L R *jo "van FIG.1

AMPLIFIER ELECTRO- MECHANICAL- MECHAN CAL ELECTRIC TRANSDUCER 5TRANSDUCER FIG. 2

CONTROL DEVICE OSCILLATING BODY PATENTH] l 6 i975 SHEET 2 OF 5 PATENTEDSEP I 61975 E's-1cm PATENTEU SEP 1 61975 sum u of 5 il JTVQ $55 T; TVQWTTV @m m4! x mm i q d ibll zi g T; T F E: an a ww mm Q a n? ELECTRONICrnvmrlacs BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to an electronic timepiece such as abalance-hairspring-driven electronic timepiece, tuning fork orsound-piece-driven electronic timepiece or crystal oscillator electronictimepiece comprising an electronic circuit formed in a monolithic chipwithout using any other electronic parts.

2. Description of the Prior Art An electronic timepiece heretoforeproposed comprises an electronic circuit which must be provided with aplurality of electronic parts inclusive of a semiconductor chip.

In FIG, I is shown an electronic circuit of a balancehairspring-drivenelectronic timepiece heretofore proposed. In FIG. I, Q designates atransistor, R a base bias resistor, C a condenser for defining a timeconstant, Cx a condenser adapted to prevent an abnormal oscillation, L;a detecting coil, L a balance-hairspringdriving coil, and V an electricpower source.

In the bipolar type transistor, in general, a forward direction voltagebetween the base and the emitter is 0.4 to 0.5V when a small currentflows therethrough. This bipolar type transistor is designed such that anecessary bias voltage applied to its base causes the forward directionvoltage to increase, to an active region from a minute amplitude. Thisrole is played by the resistor R and the condenser C in the electroniccircuit shown in FIG. 1. As seen from the above, in the conventionalelectronic circuit, a time constant circuit composed of the resistor Rand the condenser C produces the base bias voltage in response to theamplitude of the balance hairspring so as to maintain the amplitude at aconstant value. The condenser Cx plays the role of constituting a bypathfor preventing the abnormal oscillation of the electronic circuit.

In the electronic circuit shown in FIG. 1, the practical value of thecondenser C is C=O.47 P, the practical value of the resistor R is R=l0M9. and Cx=200pF. r

These practical values of the condenser C and the resistor R aredetermined by the balance hairspring driving frequency 5 to 6 Hz (period0.2 second). In addition, the time constant CR is given by CR=O.47 l0 X10 X I0 4.7 sec., that is, about 25 times the balance hairspring drivingperiod.

If the condenser is formed in the same one semiconductor chip as thetransistor, the space required becomes so large that, in practice, theupper limit of the capacity of the condenser is several hundreds pF. Asa result, if it is desired to make the capacity value of the condenser Csmall, with the product of the condenser C and the resistor R keptconstant, the resistor R must necessarily be large in value. Too large aresistor R, however, results in a limitation of the base current of thetransistor. As a result, it becomes difficult to obtain a sufficientlylarge collector current, that is, a balance hairspring driving currenteven if use is made of a transistor having a large amplification factor.In addition, even if a desired valve condenser were formed in asemiconductor chip, it is difficult to obtain the value of the resistorR IOMQ where use is made of the general diffusion resistor, because theresistance value of diffusion resistors is limited to at most severaltens K!) to IOOKQ because of restrictions in the available area. As aresult, it is practically impossible to form the transistor, condenserand resistor of the balance hairspring driving type electronic timepieceas such shown in FIG. 1 all in a monolithic chip. Thus, use must be madeof a plurality of electronic parts in order to construct the electroniccircuit shown in FIG. 1. In practice, therefore, the transistor,condenser and resistor are individually connected to printed wiringformed on a ceramic substrate so as to form a mixed integrated circuit.

Such mixed integrated circuit composed of a plurality electronic parts,however, has the disadvantages that the circuit is large in volume, thatthe overall reliability of the circuit is decreased with the increase ofthe number of the electronic parts, and that the manufacturing costbecomes high due to the increase of the number of assembling steps.

In general, the resonance frequency of an oscillating body is a functionof the amplitude of the oscillation of the oscillating body. When anoscillating body is used as a speed governor, it is desired to cause theoscillating body to always oscillate with a constant amplitude. Theamplitude the oscillation of the oscillating body reaches to a steadystate at a point at which the driving energy which is the function ofthe amplitude of the oscillation of the oscillating body balances withthe lost energy of the oscillating body. Under such conditions much ofthe electric power is consumed so that such oscillating bodies areseldom used with a timepiece.

In general, the relation in function between the amplitude and thedriving energy is so changed that the amplitude of the oscillating bodybecomes the steady state at a defined amplitude.

As described above with references to FIG. 1, the method heretoforeproposed exclusively makes use of the fact that the diode in the forwarddirection between baseemitter and between base-collector of the bipolartransistor is capable of clamping a detecting signal to produce a directcurrent component, that the condenser is charged with the direct currentcomponent thus produced, and that the apparent bias voltage supplied tothe input part of the transistor is decreased in response to theincrease of the amplitude of the oscillating body, thereby decreasingthe driving pulse width. This method, however, is required to maintainthe applied direct current component for a time longer than the periodof the oscillating body, and as a result, the time constant ofdischarging the condenser must be large. Thus, it is necessary to use aresistor having a large resistance value and a condenser having a largecapacity. In the present semiconductor technique, it is almostimpossible to manufacture the above described high ohmic resistor andlarge capacity condenser. As a result, an electronic circuit for use inelectronic timepieces and including such high ohmic resistor and largecapacity condenser could not be realized.

SUMMARY OF THE INVENTION This invention obviates the above describeddisadvantages of the conventional electronic timepiece and for thispurpose an electronic circuit is formed in a monolithic chip An objectof the invention, therefore, is to provide an electronic timepiece whichcomprises an electronic circuit formed in a monolithic chip, and whichcan make the electronic circuit small in volume and can make the numberof the parts included therein small, thereby improving the overallreliability in operation of the electronic circuit.

The invention provides an electronic timepiece which makes use of asignal corresponding to the differentiation of a detecting signal so asto control .the bias potential supplied to the input part of anamplifier and which can control the amplitude of an oscillating bodyimmediately before a driving pulse is obtained such that the requisitetime constant is considerably smaller, thereby obviating the need for alarge capacity condenser.

The invention also provides an electronic timepiece comprising anelectronic circuit which includes passive elements whose resistorelement is composed of MOS-R (Metal-Oxide-Silicon Resistor) and whosecapacity element is composed of a semiconductor of MOAOS (Metal-Oxide-AlO -Oxide-Silicon) struction and an active element consisting of abipolar type transistor, and which can provide a combination of a highresistance resistor element, a capacity element having an excellentvoltage-capacity characteristic within an operating range, and a bipolartype transistor, which is difficult to obtain by the prior art techniqueof manufacturing a semiconductor.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an electronic circuit diagramof a conventional balance-hairspring-driving type electronic timepiece;

FIG. 2 is a block diagram illustrating the construction according to theinvention;

FIG. 3 is a signal waveform diagram illustrating the operation of theconstruction shown in FIG. 2;

FIG. 4 is a signal waveform diagram illustrating the operation ofanother embodiment of the invention;

FIG. 5 is an electronic circuit diagram of an embodiment of theinvention;

FIG. 6 is a perspective view of a MOS (Metal-Oxide- Silicon) transistorused in the electronic circuit shown in FIG. 5, a part being shown insection;

FIG. 7 is a partial longitudinal sectional view of a MOAOS constructionused in the electronic circuit shown in FIG. 5;

FIG. 8 is a graph showing a voltage-capacity characteristic of asemiconductor;

FIGS. 9 (1) to 9(11) are cross-sectional views of a portion of theelectronic circuit according to the invention illustrating successivemanufacturing steps thereof.

DETAILED DESCRIPTION OF THE INVENTION input part of the amplifier l isalso supplied as a control signal through a control devide 5 having botha differentiating function and an amplifying function to the input biaspart of the amplifier 1.

An embodiment of the invention will now be described with reference tothe signal wave diagram shown in FIG. 3 and illustrating the operationof the construction shown in FIG. 2.

In FIG. 3 A(a) is shown the embodiment of obtaining the detecting signalcorresponding to the angular velocity of the overall period of theoscillating body 3. Let it be assumed that the detecting signal f(A)obtained is in its steady state. Its differentiated wave f '(A) is shownin FIG. 3 A(b). From this difierentiated wave j (A) is obtained acontrol signal for the time 'r at which the differentiated wave f'(A)exceeds the threshold level The of the control device 5. If the controlsignal from the control device 5, for example, causes the bias potentialat the input part of the amplifier 1 to go completely to zero, this biaspotential has a low level during the time T and then increases towardsthe initial bias level with the time constant of the input part of theamplifier l as shown by broken lines V in FIG. 3A(c). To this biaspotential is added the detecting signal delivered from the mechanicalelectric transducer 4 in an alternating current to produce a resultantpotential shown by a full line in FIG. 3 I(c). From this resultantpotential is obtained a driving signal pulse for that time 1,, at whichthe resultant potential exceeds the threshold level Thp of the amplifier1 shown by broken lines in FIG. 3A(c).

If the amplitude of the oscillating body 3 becomes smaller, the width1",, of the driving pulse is increased as shown in FIG. 3B, and as aresult, to the oscillating body 3 is applied a larger driving energywhereby the amplitude of the oscillating body 3 is increased.

On the contrary, if the amplitude of the oscillating body 3 becomes toolarge, the width 1",, of the driving pulse is decreased as shown in FIG.3 C or eventually ceased to exist, and as a result, to the oscillatingbody 3 is applied a smaller driving energy whereby the ampli tude of theoscillating body 3 is decreased or restricted.

A ratio of the change in the driving pulse width 'r to the variation inthe amplitude of the oscillating body 3 in and about its steadyoscillating state may be changed by the time constant of the input partof the amplifier 1, by the level 1 shown in FIG. 3 B at which thecontrol signal becomes zero and the direct current bias level begins toraise, by magnitude of the detecting signal and the like. Thus, aselection of variables of respective parts of the construction accordingto the invention mades it possible to obtain an optimum ratio of thechange in the driving pulse 1",, to the variation in the amplitude ofthe oscillating body 3. As seen from the above, the invention is capableof controlling the driving pulse just prior to obtaining it, therebyobtaining the object aimed at with the aid of extremely small timeconstant. I

Another embodiment of intermittently obtaining the detecting signal willnow be described with reference to FIG. 4.

In the present embodiment, the driving signal is obtained at thoseportions h I1 and 11;, of the intermittent detecting signal f(A) whichcorrespond to the tops of the detecting signal wave f(A) shown in FIG.4(a). The control signal is obtained at those portions of theintermittent differentiated wave f(A) which correspond to positionsshown by 11-, and 11 in FlG. 4(b). As a result, the driving signal iscontrolled at, at least, two points h and 11 thereby significantlyimproving the efficiency.

If the driving signal is controlled at points h h, and h for example,respectively, the driving signal is over controlled at the point h suchthat a sufficiently large driving energy can not be applied to theoscillating body 3 at its starting time. It is a matter of course thatif the driving signal is controlled at the point 11 only, a sufficientcontrol can not be effected of the driving signal at the point h At theother points, the driving sig nal is controlled in the manner similar tothe above.

FIG. ,5 shows an electronic circuit for controlling the driving signal.

Referring to FIG. 5, Q Q and Q designate transistors for contituting anamplitude control circuit, O to Q transistors for consituting amplifierand driving circuits, and L, a detecting coil. The minute detectingvoltage obtained from the detecting coil L is applied through acondenser C to the amplifier circuit. A voltage amplification of thisminute detecting voltage is effected by the transistors Q, to Q and acurrent amplification thereof is effected by the transistors Q and Qthereby operating a driving coil L The voltage for driving the drivingcoil L is fed back through a resistor R to the input part of theamplifier circuit. The resistor R and the condenser C constitute a timeconstant ciruit which is capable of applying a bias voltage to the baseof the transistor Q The minute detecting voltage obtained from the detecting coil L is also applied through a differentiatingnetworkcondenser C to the base of the transistor Q of the amplitude controlcircuit whose transistor Q serves to amplify this detecting voltage.When detecting voltage thus amplified exceeds a given value, thetransistor Q becomes conductive to change the bias voltage supplied tothe base of the transistor Q The use of measures described above ensuresa more positive control of the amplitude of the balance hairspring ofthe timepiece than the base bias control circuit composed of thecondenser C and the resistor R only and further provides the importantadvantage that the consumed current becomes small.

In the electronic circuit shown in FIG. 5, the maximum capacity of thecondenser C may be made 200 pF. As a result, such maximum capacity maybe obtained by the capacity of a semiconductor. The resistance value ofthe resistor R must be made on the order of 1000 M!) which could not beobtained in practice by customary diffused resistors. The inventionmakes use of MOS-R (Metal-Oxide-Silicon--Resistor) technique in order toobtain the resistor R whose resistance value is on the order of 1000 M9.

An electronic circuit adapted to drive the hairspring balance and formedin a monolithic chip on the basis of the MOS-R technique and a method ofmanufacturing it wil now be described with reference to FIGS. 6 to 9.

In principle, the MOS-R (MetaLOxide-Silicon) technique makes use of anon-linear voltage-current characteristic exhibited between twoterminals of a depletion type MOS (Metal-Oxide-Silicon) transistor(abbreviated as MOST) having a gate of P channel MOAOS (Metal-Oxide-Al-O -Oxide Silicon) construction as a highly resistive resistor whoseresistance value is on the order of 1000 MD, one of the two terminalsbeing a drain region and the other terminal being a source regionshort-circuit to a substrate of semiconductor material and a gate. I g

The invention makes use of a method of manufacturing MOST comprising astep of incorporating a highly resistive resistor into a silicon chipwhich is the same as a bipolar transistor shown in FIG. 6.

Referring to FIG. 6, reference numeral 6 designates a source, 7 a gate,8 a drain, 9 an oxide film, and 10 a N type substrate.

In order to use MOS-R (Metal-Oxide-Silicon-- -Resistor) as a highlyresistive resistor, MOST (Metal- Oxide-Silicon Transistor) must beprovided with a gate of P channel MOAOS (Metal-Oxide A1 O -Oxide-Silicon) construction as will be described.

In FIG. 7 is shown a MOAOS (Metal-Oxide-A O Oxide-Silicon gate composedof five layers consisting of an aluminum electrode M, a protective oxidefilm 0', an alumina film A, a first layer oxide film O and a siliconsubstrate S viewed from the above. The silicon substrate S is of Nconductivity type and the first layer oxide film O is a SiO filmthermally oxidized on the silicon substrate S. The thickness of'thisthermally oxidized film O is capable of controlling the resistance valueof the MOS-R.

An example between the thickness of the thermally oxidized film O andthe resistance value of the MOS-R (Metal-Oxide-Silicon Resistor) isshown in the following Table.

TABLE Thickness of thermally Resistance value (voltage across In theabove Table, the specific resistance of the N type silicon substrate is5 Qrcm, the thickness of the alumina film is 2000 A, the thickness ofthe protective SiO film is 1000 A, and W/L of the MOS-R(Metal-Oxide-Silicon-Resistor) is l/200 (W is a width of the gate 7 andL is its length as shown in FIG. 6).

In general, the thickness of the alumina film A has less influence uponthe resistance value of the MOS-R (Metal-Oxide-Silicon-Resistor). It ispreferable to treat the alumina film A at a low temperature, because ahigh temperature treatment causes the alumina film to be hardened whichmust be avoided if an etching treatment is to be used. The protectiveSiO film O is deposited from a vapor phase on the alumina film A. Asdescribed above, the alumina film A is subjected to the low temperaturetreatment so as to easily effect the etching treatment. The alumina filmA subjected to the low temperature treatment is liable to be extremelysensitive to after treatments.

For example, if the alumina film A is formed by thermally decomposingaluminum isopropylate or aluminium ethylate at a temperature lower than800C, there is a risk of the alumina film A thus formed being easilyaffected by a etching bath used in the etching treatment of formingcontact holes or etching aluminum. In the present invention, in order toavoid such disadvantage, the alumina film A is covered with theprotective SiO film O deposited thereon from vapor phase.

The P channel MOST (Metal-Oxide-Silicon Transistor) having the MOAOS(METAL-OXIDE-Al O -OXIDE-SILICON)- gate constructed as above describedis of depletion type. As shown in the above Table, if the thickness ofthe first SiO film is larger than 500 A, the resistance value becomesinfinitely large so that the MOST becomes enhancement type in which nocurrent flows. As a result, provision may be made of a MOAOS gate havinga resistor portion upon the completely exposed silicon surface and theother portions having excess oxide of a thickness of at least 500 A, nocurrent flows through the MOAOS. In addition, the gate portion of theMOS-R may be used as a condenser.

The invention makes use of a N channel type semiconductor capacitycharacteristic by taking its capacity-voltage characteristic (C-Vcharacteristic) into con sideration. That is, the N channel typesemiconductor capacity incorporated at the time of manufacturing theMOST-R is of enhanced type having a good C-V characteristic in theoperating voltage range shown in FIG. 8.

A method of manufacturing the electronic circuit embodying the inventionshown in FIG. will now be described.

Constitutional elements formed in a monolithic chip (silicon chip in thepresent embodiment) are a NPN bipolar transistor, a PNP lateral bipolartransistor, a MOS-R of P channel MOAOS construction, and a condenser ofN channel MOAOS construction. Steps of manufacturing theseconstitutional elements will now be described with reference to FIG. 9.

As shown in FIG. 9 (l), a P type silicon is thermally oxidezed to forman oxide layer and the oxide layer thus formed is etched to cut a givennumber of holes. Then, a donoer element compound having a small thermaldiffusion constant such as antimony and the like is diffused into the Ptype silicon. Reference numeral 31 designates a N layer thus diffusedinto the P type silicon and usually called as an buried layer. This N*layer 31 is capable of lowering the saturated collectoremitter voltageVces of the NPN transistor and of eliminating a parastie transistor incase of using the lateral PNP transistor.

As shown in FIG. 9(2), SiO grown in the step shown in FIG. 9(1) iscompletely removed and then a N type silicon epitaxial layer 32 is grownon the P type silicon as well as on the diffused N layers. The thicknessof the N type silicon epitaxial layer 32 is larger than about microns.It is necessary to make the specific resistance of the N type siliconepitaxial layer 32, l to SQ-cm in consideration of the characteristicsof the transistor and MOS-R.

In the step shown in FIG. 9(3), a thermal oxidation is effected toproduce an oxide film and then the oxide film thus produced is etched toform a given number of holes 33. A compound of an accepter element suchas boron and the like is thermally diffused into the N type siliconexpitaxial layer 32 until the thermally diffused regions reach to thesurface of the starting P type silicon substrate. This step is so-calledisolation diffusion and is capable of isolating the N type zones asislands surrounded by these diffused zones.

In the step shown in FIG. 9(4), the SiO layer 35 formed by the stepshown in FIG. 9(3) or a SiO layer newly grown is subjected to aphotoetching process to form a given number of holes. Through theseholes is thermally diffused a compound of an accepter element such asboron and the like to form a PN junction or junctions 36 in therespective islands until the PN junc-' tion or junction 36 reach to agiven depth (usually 2 to 3 These P type diffused zones form a baselayer of the NPN transistor, a collector layer and an emitter layer ofthe PNP transistor, two terminals of the MOS- R, and a lower electrodeof the MOS-C (N-channel type C improves the C-V characteristic).

In the step shown in FIG. 9(5), a photoetching process is subjected tothe SiO layer 38 formed during the step shown in FIG. 9(4) or to a newlygrown SiO layer to form a given number of holes. Through these holes isthermally diffused a compound of a donner element to form a PN junction38 until the PN junction 38 reaches to a given depth (usually 2 to 3p).These N type diffused zones form an emitter layer and a collectorcontact of the NPN transistor, a base contact of the PNP transistor, anda substrate contact of the MOS-R. Particularly, the steps shown by FIGS.9(4) and 9(5) serve to determine the electric characteristics such as h(grounded emitter current gain) and the like of the NPN transistor sothat the thermal diffusion of these steps must be effected withparticular care.

A feature of the invention is the provision of the above described stepsof simultaneously forming in the N type silicon a PNP transistor, twoterminals of MOS-R and two terminals of MOS-C with a NPN transistor.

In the step shown in FIG. 9(6), the SiO; layer formed by the step shownin FIG. 9(5) or a newly grown SiO layer is subjected to a photoetchingprocess to form a given number of holes for the purpose of forming aMOS-R and MOS-C. This step of forming the holes must be effected in amanner such that residual SiO becomes absent. In addition, it ispreferable to make holes at those portions of the SiO; layer whichcorrespond to the contact holes for the purpose of simplifying themanufacturing steps to be effected.

In the step shown in FIG. 9(7), a growth of the first SiO layer iseffected. For example, the first SiO layer Whose thickness is about 200A is grown by an oxidation at a temperature of 700C for 20 minutes.

In the step shown in FIG. 9(8), the alumina film is formed and a heattreatment is carried out on it. It is preferable to use an organicaluminum as an almina source and thermally decompose it and deposit itfrom vapor phase. For example, aluminum isopropylate or aluminumethylate is vaporized with the silicon substrate heated at a temperatureof about 420C to deposite the alumina film of about 2000 A and then thealumina film thus deposited is heat-treated at a temperature of 750C inN atmosphere for about 30 minutes.

In the step shown in FIG. 9(9), the protective SiO film is depositedfrom vapor phase. Its heat treatment has usually been effected at atemperature on the order of 900C for the sake of safety. As abovedescribed, the alumina film treated at a high temperature causes it tobe hardened which makes the etching treatment to be effected diffieult.As a result, the protective SiO film is heat-treated at a temperature onthe order of 750C for 30 minutes in 0 atmosphere. The protective SiOfilm thus being formed can sufficiently protect the alumina film frombeing affected by the etching bath. It is preferable to make thethickness of the protective SiO film on the order of I000 A because theprotective SiO film could not protect the alumina film from beingaffected by the etching bath if the thickness of the protective SiO filmbecomes too thin. In the step shown in FIG. 9(10), the etching processis effected so as to form contact holes through which are led outaluminum elecrodes by the next step. In the well known steps, layers tobe formed with the contact holes has a multiplicity of layers composedof a protective SiO film, an almina film, a first Si film, andsuperimposed SiO, films formed in the steps shown in FlGS.,9( l to 9(5)(those SiO films areabsent at the MOS-R part), and as a result, thesuitable etching solution must frequently be prepared.

On the contrary, the invention provides the holes for those portionscorresponding to the contact holes by the step shown in FIG. 9(6) forthe purpose of forming the MOS-R and MOS-C. As a result, layers'of theportions corresponding to the contact holes has three layers composed ofthe protective a Si0 film, and an alumina film and a first SiO film.

In case of effecting the etching process, in the first place theprotective SiO film is covered with a resist and then contact holes areformed in the protective SiO film by acidic ammonium fluoride solution.Then, the resist is removed by H 80 H O solution. It is preferable touse KPR (Kodak Photo Resist) as the resist. When the resist is removed,the alumina film is simultaneously removed as a result a SiO film havingan extremely thin thickness of the order of l()() to 200 A remains.Then, use is made of a P-etching solution whose rate of etching the SiOfilm is low. The SiO film remained on the overall surface becomes thinso that it is preferable to make the SiO film which the contact holesare not formed sufficiently thick beforehand.

In the step shown in FIG. 9(11), aluminum is deposited and thensubjected to the etching process to form electrodes 41.

The bipolar technique heretofore proposed determines the temperature andtime necessary for the heat treatment or so-called sintering treatmentby taking the sufficient alloying between aluminum and silicon intoconsideration and hence the heat treatment is effected at 400C for 30minutes.

On the contrary, in the present invention the gate part of the MOS-Rmust be sufficiently sintered, other wise the resistance value of theMOS-R becomes unstable. Experimental tests have yielded satisfactorygood results when the gate part is sintered at 475C for 90 minutes. inaddition, such sintering treatment does not give much influence upon thecharacteristic of the bipolar element.

In FIG. 9(11), reference numerals 51 and 52 desig nate electrodeterminals of the MOS-R, 53 an electrode terminal of the P type siliconsubstrate, 54 an electrode terminal of the NPN transistor base, 55 anelectrode terminal of the NPN transistor emitter, 56 an electrodeterminal of the NPN transistor collector, 57 an electrode terminal ofthe PNP transistor base, 58 an electrode terminal of the PNP transistoremitter, 59 an electrode terminal of the PNP transistor collector, and60 and 61 electrode terminals of the MOS-C.

As stated hereinbefore, the use of the electronic circuit describedensures a decrease of the capacity of the condenser to the order of200?, and a production of a highly resistive resistor and provides theimportant advantage that an electronic circuit for use in balancehairspring driving type electronic timepieces can be formed in amonolithic chip, that is, in the same single chip. The electronictimepiece formed in the monolithic chip is far superior in massproduction scale, reliability, volume density, cost and the like to theconventional electronic watch composed of a multiplicity of electronicparts and the former is significantly improved in function if comparedwith the latter.

The monolithic chip in which the electronic circuit for use in balancehairspring driving type electronic timepieces shown in FIG. 5 wasincorporated as described above may also be applied to an electroniccireuit for use in tuning fork driving type electronic timepieces. lnaddition, the MOS-R technique described above is capable ofmanufacturing an electronic circuit for use in crystal oscillator typeelectronic timepieces. It is a matter of course that the monolithic chippermits of obtaining all types of electronic timepieces.

.What is claimed is:

1. An electronic timepiece, comprising:

an electromechanical transducer for converting an electric signal intomechanical energy;

an oscillating body connected to said mechanical transducer and drivenby said mechanical energy to an amplitude dependent upon the energy of asignal applied to said transducer; mechanical-electrical transducercoupled to said oscillating body for generating an electric feedbacksignal having an amplitude corresponding to the displacement of saidoscillating body;

a feedback amplifier responsive to said feedback signal and connectedbetween said mechanicalelectric transducer and said electro-mechanicaltransducer for applying an electrical signal to the latter, saidamplifier having a variable bias;

a control circuit including a first amplifier means connected to saidmechanical-electrical transducer by a differentiating means andenergized by said feedback signal, said first amplifier means beingconnected to said feedback amplifier for varying said bias thereof, saidamplifier and said control circuit being formed in a monolytic chipwhereby the bias of the feedback amplifier is responsive to thedifferential of said feedback signal to control oscillation of theoscillating body.

2. The electronic timepiece defined in claim 1 wherein said feedbacksignal is an alternating current signal.

3. The electronic timepiece defined in claim 1 wherein said firstamplifier includes a plurality of NPN transistors in cascade with thecollector of each transistor connected to the base of a successivetransistor, the base of the first transistor being energized throughsaid first capacitor from said mechanical electrical transducer and thecollector of the last transistor forming an output terminal;

said feedback amplifier includes a plurality of other pairs of NPNtransistors with a first transistor of each pair having an emitterconnected to the base of the second transistor of each pair and theircollectors tied together and to the base of the first transistor of asuccessive pair, said output terminal being connected through a resistorto the base of the first transistor of the first pair and saidmechanical electrical transducer being connected via a second capacitorto the base of the first transistor of the first pair;

said timepiecefurther including another NPN transistor having its baseconnected to the collector of the last transistor of the last pair, andthe last NPN transistor in the last pair having its base connected tothe emitter of said other transistor in the last mentioned pair, a PNPtransistor having its base connected to the collector of said lastmentioned transistor and said first NPN transistor in the said feedbackamplifier having a base connected to the collector of said PNPtransistor and the emittercollector electrodes of said PNP transistor incircuit with said electromechanical transducer.

4. The electronic timepiece defined in claim 3 wherein said circuitincludes as its passive element a resistor element composed of anelement whose one terminal is a drain of a depletion type MOST (Metal-Oxide-Silicon structure type transistor) and the other terminal is aconnection of a source, gate and substrate thereof and as a capacityelement an element composed of a semiconductor element of MO-AOS (Metal-

1. An electronic timepiece, comprising: an electromechanical transducerfor converting an electric signal into mechanical energy; an oscillatingbody connected to said mechanical transducer and driven by saidmechanical energy to an amplitude dependent upon the energy of a signalapplied to said transducer; a mechanical-electrical transducer coupledto said oscillating body for generating an electric feedback signalhaving an amplitude corresponding to the displacement of saidoscillating body; a feedback amplifier responsive to said feedbacksignal and connected between said mechanical-electric transducer andsaid electro-mechanical transducer for applying an electrical signal tothe latter, said amplifier having a variable bias; a control circuitincluding a first amplifier means connected to saidmechanical-electrical transducer by a differentiating means andenergized by said feedback signal, said first amplifier means beingconnected to said feedback amplifier for varying said bias thereof, saidamplifier and said control circuit being formed in a monolytic chipwhereby the bias of the feedback amplifier is responsive to thedifferential of said feedback signal to control oscillation of theoscillating body.
 2. The electronic timepiece defined in claim 1 whereinsaid feedback signal is an alternating current signal.
 3. The electronictimepiece defined in claim 1 wherein said first amplifier includes aplurality of NPN transistors in cascade with the collector of eachtransistor connEcted to the base of a successive transistor, the base ofthe first transistor being energized through said first capacitor fromsaid mechanical electrical transducer and the collector of the lasttransistor forming an output terminal; said feedback amplifier includesa plurality of other pairs of NPN transistors with a first transistor ofeach pair having an emitter connected to the base of the secondtransistor of each pair and their collectors tied together and to thebase of the first transistor of a successive pair, said output terminalbeing connected through a resistor to the base of the first transistorof the first pair and said mechanical electrical transducer beingconnected via a second capacitor to the base of the first transistor ofthe first pair; said timepiece further including another NPN transistorhaving its base connected to the collector of the last transistor of thelast pair, and the last NPN transistor in the last pair having its baseconnected to the emitter of said other transistor in the last mentionedpair, a PNP transistor having its base connected to the collector ofsaid last mentioned transistor and said first NPN transistor in the saidfeedback amplifier having a base connected to the collector of said PNPtransistor and the emitter-collector electrodes of said PNP transistorin circuit with said electromechanical transducer.
 4. The electronictimepiece defined in claim 3 wherein said circuit includes as itspassive element a resistor element composed of an element whose oneterminal is a drain of a depletion type MOST (Metal-Oxide-Siliconstructure type transistor) and the other terminal is a connection of asource, gate and substrate thereof and as a capacity element an elementcomposed of a semiconductor element of MO-AOS(Metal-Oxide-Al2O3-Oxide-Silicon) structure type, an upper metal of saidsemiconductor element being one terminal and an under silicon layerthereof being the other terminal.
 5. An electronic timepiece as definedin claim 3 wherein said electronic circuit includes as its passiveelement a resistor element composed of a depletion type MOST(Metal-Oxide-Silicon structure type transistor) and includes as itsactive element a bipolar type transistor.